Process for spinning filaments



Aug. 29, 1967 I E. VANCE r 3,339,000

PROCESS FOR SPINNING FILAMENTS Filed Oct. 10, 1963 INVENTOR E RIC VANCE QML/ BY ATTORNEY United States Patent 3,339,000 PROCESS FOR SPINNING FILAMENTS Eric Vance, Waynesboro, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 10, 1963, Ser. No. 315,179 3 Claims. (Cl. 264-184) This invention relates to a wet spinning process for preparing filaments from segmented elastomers. More particularly, it relates to the wet spinning of a tow of continuous filaments from solutions of synthetic, segmented, elastic polymers.

In the wet spinning process for forming fibers, a polymer solution is extruded through an orifice into a setting or coagulation bath. This coagulation bath generally contains a mixture of a solvent for the polymer and a liquid miscible with the solvent. The fiber is formed as the solvent diffuses out of the extruded polymer stream into the bath.

It is old in the art to wet spin bundles of filaments of segmented elastomers. Immediately upon extrusion, the filaments are quite tacky; and if it is desired to produce a bundle of coalesced filaments, it is a relatively simple matter to bring the individual filaments together for purposes of coalescence. If, on the other hand, a tow or bundle of separate, continuous filaments is desired, care must be taken to prevent the filaments from sticking together. In the past, a particulate solid material, for example, talc, has been dispersed in the coagulation bath at levels of 510% to prevent interfilament adhesion during spinning and extraction of residual solvent from the tow of elastic filaments. The use of a dispersed solid material in this Way produces an opaque coagulation bath. The opacity of the bath interferes with the detection of faulty spinnerets and observation of the threadline action and guide alignment during spinning. Moreover, when talc is used as the dispersed solid material, there are the following disadvantages: a serious housekeeping problem with talc spattered about the equipment is encountered; the tale must be filtered off before the solvent is easily recovered from the bath overflow liquor; talc carries over on the threadline into the extraction baths, fouling the shaft seals and creating a maintenance problem; and the high bath temperatures, which appear to be essential to the efiectiveness of a talc suspension, cause increased vaporization of solvent from the bath and require special ventilation of the spinning area.

It is an object of this invention to provide a wet spinning process for preparing a tow of segmented elastomer. Anotherobject is to obviate the need for use of a particulate, dispersed solid material in the coagulation or extraction baths in the wet spinning of spandex tows.

These and other objects are accomplished by a process for wet spinning a bundle of filaments of segmented elastomer in coagulation and extraction baths free of dispersed solid material which comprises (a) extruding a segmented elastomer dissolved in a solvent therefor through a spinneret into a coagulation bath consisting solely of liquids which is maintained at a temperature less than 60 C. to form a plurality of filaments which have a breaking elongation greater than 200%, (b) stretching the filaments from about 1.5 to about 3.0 times their extruded length while passing them through and withdrawing them from the coagulation bath, (c) washing the filaments in a bath which is maintained at a temperature less than 60 C. to substantially remove the solvent while maintaining the filaments in a stretched condition, (d) applying a finish to the washed filaments while maintaining them in a stretched condition, and (e) recovering a bundle of elastomeric filaments free from appreciable interfilament adhesion. It has been discovered that by maintaining the coagulation and extraction baths at temperatures below 60 C. and by keeping the tow stretched during coagulation and extraction, the use of dispersed solid material in the baths may be dispensed with.

The results will be better understood by referring to the accompanying drawing which is presented for purposes of illustration. In the drawing, the figure is a diagrammatic view of suitable apparatus for carrying out the process of this invention. The polymer solution is forwarded (by pump 10 through solution heater 12 and through candle filter 14 to spinneret 16 containing a large number of orifices, from which it is extruded into coagulation bath 18. The extruded solution is converted to filament bundle 20 by loss of solvent to the bath. The filament bundle passes through the bath and through convergence guide 22 and is withdrawn from the bath by passage around roll 24, which provides the necessary stretch to the bundle. The stretch may be conveniently monitored for a given type of elastic filament by observing the tension on the advancing threadline with tension measuring device 26. The liquid in coagulation bath 18 is kept at the desired concentration by being continuously renewed through inlet 23 and removed through outlet 25.

The tow is passed through extraction baths 28, 30 and 32 to effect substantially complete removal of the solvent. The bundle of filaments may .be passed several times through each stage of the extraction baths in order to increase the length of travel in the baths, and is finally removed by roll 34, proceeding to roll 36 after passing through finish bath 38. The speed of the various rolls is adjusted so as to provide and maintain the requisite stretch at the various stages in the operation. From roll 36, the filament bundle passes between stripper pins 40 for removal of excess finish and is then relaxed by passage over rolls 42. The tow with finish applied is finally deposited continuously on conveyor belt 44 and passed through a drier, not shown.

The segmented elastomer which makes up the filament bundle consists of segments of a high-melting, crystalline polymer alternating with segments of a low-melting, amorphous polymer. The crystalline, high-melting segment may be derived from, for example, a polyurea, polyurethane, polyamide, bis-ureylene polymer, or polyester. The low-melting, amorphous segment may be derived from, for example, a polyester, a polyether, or a hydrocarbon polymer. Polymers of the spandex type are illustrative of such a segmented elastomer.

The segmented copolymers described in several patents are useful in the practice of this invention. Among these are US. Patents 2,929,801; 2,929,802; 2,929,803; 2,929,- 804; 2,957,852; 2,962,470; 3,009,901; 3,040,003; 3,044,- 987; and 3,044,989. As disclosed in these references, such segmented copolymers when in filament form display elongations at the break in excess of 200%. Although these segmented elastomers are described as substantially linear, it is not intended that segmented copolymers which have some branches extending from the polymer chain be excluded.

The solution of segmented elastomer may be prepared by direct polymerization in the solvent or, alternatively in some cases, by dissolving the polymer in the solvent. For elastomers which cannot be dissolved in the solvent, the solution may be prepared by carrying out the final step of the polymerization in the presence of the solvent. Even for soluble polymers, the latter method is the preferred technique. Suitable solvents are water-miscible compounds having a dipole moment greater than 3.5, which have no active hydrogen atoms but have donor oxygen atoms for hydrogen bonding. Examples are dimethylformamide, dimethylacetamide, dimethylpropion- -spinning speeds with good continuity. Substantial attainment of these effects occur when the polymer solution temperature is at least 70 C. at the spinneret. The temperature of the preheated solution should not exceed 105 C. Preferably, thetemperature is about 90 C.

Except for the critical features of temperature of the baths and stretching the tow, the wet spinning process of this invention is carried out in a conventional manner. It is preferable that the concentration of polymer in solution be between and 30% by weight although solutions of less than 5% can be spun, and the only limiting factor on the upper level of the concentration is the stability of the polymer solution to gel formation or precipitation from solution before spinning.

The coagulation bath is generally water, or a mixture of water and polymer solvent, but other solvent-miscible liquids are feasible for use in the coagulation and extraction baths. The length of travel of the threadline in the bath will depend upon the rate of extrusion and the rate of windup, the temperature of the coagulation bath, and the concentration of the polymer solution being spun.

For the practice ofthis invention,,the temperature of the coagulation bath must be kept below 60 C. Preferably the temperature'is kept below 40 C. The optimum bath temperature will depend upon the nature and concentration of the polymer being spun, the nature of the solvent used, and the concentration of solvent in the coagulation bath. The temperature must, of course, be above the freezing point of the combined constituents.

In similar manner, the temperature of the extraction bath or baths, if any are used, must be kept below 60 C. in order to avoid the use of dispersed solids such as talc. Lower. temperatures are preferred, again less than 40 C., but not below the freezing point of the combined constituents. Since the diffusion of residual solvent from the tow occurs more slowly at the lower temperature, multiple wraps of the tow on the extraction rolls are useful in order to increase the extraction efficiency of a given apparatus. Multiple-stage, countercurrent extraction may also be used. As. is well known, liquid carry-over by the tow from stage to stage should be minimized, such as by the use of baffles. The extraction of solvent must be sufiiciently complete to give a non-sticky yarn on emergence from the extraction bath. Preferably, the extracted yarn contains less than 1% by weight of residual solvent. One of the critical operating conditions in the process of this invention is the use of a controlled amount of stretch applied to the filament bundle. The use of from about 1.5X to about 3X stretch in conjunction with low bath temperatures prevents the individual filaments in the bundle from adhering to one another and permits elimination of dispersed talc from the bath. Preferably,

the filamentbundle is stretched by an amount from 2X to 3X.

The stretch develops in the coagulation bath and may be measured by noting the surface speed of a roll over which the filament bundle is passing, and dividing by the spinning speed in the same unit of measurement. The spinning speed in yards per minute, for example, may be obtained by calculating from the delivery rate of the pump metering polymer solution to the spineret the rate of extrusion in denier-yards per minute and then dividing this figure by the final denier of the filament bundle. For

continuous operation with a given elastomeric composition, the tension in the tow which produces the desired amount of stretch may be empirically determined, and the process may then be monitored by observing the tension in the threadline at a convenient point, such as immediately on emergence from the coagulation bath.

After emergence from the extraction both, the filament bundle should be treated with a finish before it is relaxed so as to minimize interfilament adhesion in the bundle and to facilitate further processing of the bundle. The finish applied may be talc or a similar non-stick agent, or it may be a finish totally devoid of particulate solid material. The finish may be applied in any convenient manner, such as by dipping or spraying or by passage over wicks or similar devices. After application of the finish, the filament bundle ispreferably not squeezed to remove excess moisture and excess finish but instead may be passed over a series of stripper pins to remove excess finish without compaction.

After the filament bundle has been treated with a suitable finish, it is then dried at temperatures generally less than 105 C. The filament bundle may then be heat treated at temperatures between 105 C. and 150 C., if desired, to improve the physical properties in accord ance with US. Patent 3,047,909.

If a suitable finish has been properly applied, further treatment of the, tow is unnecessary for many uses. If, however, insufficient finish has been applied or, for some reason, the elastic tow has an excessive amount of interfilament adhesion, the degree of openness of the tow may be improved by passing it rapidly through an additional hot liquid bath, whereupon the combination of heat and drag separates the filaments which may be bound together. In this operation, increasing the bath temperature, speed of tow through the bath, or residence time of the tow in the bath increases the degree of openness. After such an operation, the tow must, of course, again be treated with finish and dried.

The invention will be further illustrated but is not intended to be limited by the following examples in which parts and percentages are by weight unless otherwise specified.

Example I Polytetramethylene glycol having a molecular weight of about 2000 is reacted with p,p-methylenediphenyl diisocyanate in a 1:2 molar ratio to provide an isocyanateterminated polyether. The isocyanate-terminated polyether (20 parts) is dissolved in parts of N,N-dimethylformamide and is added to a solution of 0.3 part of hydrazine dissolved in parts of dimethylformamide. The resulting solution of segmented elastomer contains approximately 19% solids. To this solution is added a slurry of titanium dioxide in dimethylformamide, a solution of poly(N,N-diethyl-beta-aminoethyl methacrylate) in dimethylformamide, and a solution of 4,4'-butylidene-bis ('6-t-butyl-m-cresol) in dimethylformamide such that the final mixture contains 5%, 5%, and 1%, respectively, of each additive based on the segmented elastomer. The viscous mixture is wet spun by extrusion through a 720- hole spinneret (orifice diameter 0.0025 inch) into an aqueous, talc-free bath containing 50% dimethylformamide, under the conditions specified below. The filaments are passed from the coagulation bath through a series of three talc-free extraction baths containing water, at the temperatures indicated below, and are then treated with a finish consisting of a dispersion of 10% tale in 50% aqueous acetone to yield a bundle containing 720 filaments of approximately 6 denier per filament. In the other runs, the temperature of the coagulation and extraction baths are varied as indicated below. In all of these runs, the filaments are extruded at a rate of 50 yards per minute and are withdrawn and extracted at a rate of 75 yards per minute, providing a stretch factor of 1.5X.

Coagulation Bath Temperature C.)

Extraction Bath Temperature C.)

Example 11 The preparation of Example I is repeated except that an equivalent amount of N,N'-diaminopiperazine is used in place of hydrazine to yield a solution of segmented elastomer. This solution is wet spun into a 720-filament tow under the conditions described in Example I except that the coagulation bath temperature is 45 C., the extraction bath is at room temperature, and the stretch factor during spinning is 3X. The tow is found to display a very low degree of stuck filaments, to display equivalent physical properties, and to process as well as similar tows wet spun with tale in the coagulation bath.

Example III The preparation of Example I is repeated to yield a solution of a segmented elastomer. The solution is preheated just before extrusion to a temperature of 104 C. and is wet spun by extrusion through a 960-hole spinneret (orifice diameter 0.0025 inch) into an aqueous talc-free bath containing 50% dimethylformamide under the following conditions:

Coagulation bath temperature C 37 Rate of extrusion y.p.m 56 Coagulation bath length ft 6 Rate of withdrawal from coagulation bath y.p.m 120 Tension on filaments leaving coagulation bath -g 375 Temperature of extraction baths C 37 Rate of withdrawal from first extraction bath y.p.m 130 Rate of withdrawal from second extraction bath y.p.m 135 Rate of withdrawal from third extraction bath The tow is passed through a finish bath as described in Example I at a rate of 144 yards per minute under a tension of 650 grams. The tow displays good elastic physical properties and a low degree of interfilament adhesion.

By the process of this invention, the need for talc or other dispersed solid in the coagulation and extraction baths in the wet spinning of spandex tow is completely eliminated. The elimination of talc permits improved control of the spinning process as well as a cleaner spinning operation.

The continuous filament tow produced by the process of this invention may be cut into staple. The elastic filaments of staple length may be blended with inelastic staple as taught in U.S. Patent 3,007,227, which blends are useful in the formation of elastic yarn. Staple blends may also be formed by proper blending of the continuous filament tow with a tow of inelastic continuous filaments and then cutting the blend of tows to staple length, as taught in U.S. Patent 3,077,006. The staple blends are useful for making a wide variety of elastic or stretchy products including woven, knitted and non-woven fabrics for use in universal fitting apparel, form-fitting upholstery, surgical stockings, and splint tapes.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for wet spinning synthetic elastic filaments comprising the steps of:

(a) extruding a segmented elastomer dissolved in a solvent therefor through a spinneret into a coagulation bath consisting solely of liquids which is maintained at a temperature less than C. to form a plurality of filaments which have a breaking elongation greater than 200%,

(b) stretching the filaments from about 1.5 to about 3.0 times their extruded length While passing them through and withdrawing them from the coagulation bath,

(c) washing the filaments in a bath which is maintained at a temperature less than 60 C. to substantially remove the solvent while maintaining the filaments in a stretched condition,

(d) applying a finish to the washed filaments While maintaining them in a stretched condition, and

(e) recovering a bundle of elastomeric filaments free from appreciable interfilament adhesion.

2. The process of claim 1 wherein said filaments are spandex filaments, the temperatures of the baths are less than 40 C., and said filaments are stretched from about two to three times their extruded length While being passed through and withdrawn from the coagulation bath.

3. The process of claim 1 wherein said coagulation bath is comprised of a mixture of dimethylformamide and water.

References Cited UNITED STATES PATENTS 2,965,437 12/1960 Blomberg 26077.5 3,047,356 7/1962 Polansky 1854 XR 3,115,384 12/1963 Cacella 18-54 XR 3,121,764 2/1964 Macura 264-181 3,136,830 6/1964 Oertel 264-184 D. I. ARNOLD, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

60 H. w. LUOKOWER, I. H. Woo, Assistant Examiners. 

1. A PROCESS FOR WET SPINNING SYNTHETIC ELASTIC FILAMENTS COMPRISING THE STEPS OF: (A) EXTRUDING A SEGMENTED ELASTOMER DISSOLVED IN A SOLVENT THEREFOR THROUGH A SPINNERET INTO A COAGULATION BATH CONSISTING SOLELY OF LIQUIDS WHICH IS MAINTAINED AT A TEMPERATURE LESS THAN 60*C. TO FORM A PLURALITY OF FILAMENTS WHICH HAVE A BREAKING ELONGATION GREATER THAN 200%, (B) STRETCHING THE FILAMENTS FROM ABOUT 1.5 TO ABOUT 3.0 TIMES THEIR EXTRUDED LENGTH WHILE PASSING THEM THROUGH AND WITHDRAWING THEM FROM THE COAGULATION BATH, (C) WASHING THE FILAMENTS IN A BATH WHICH IS MAINTAINED AT A TEMPERATURE LESS THAN 60*C. TO SUBSTANTIALLY REMOVE THE SOLVENT WHILE MAINTAINING THE FILAMENTS IN A STRETCHED CONDITION, (D) APPLYING A FINISH TO THE WASHED FILAMENTS WHILE MAINTAINING THEM IN A STRETCHED CONDITION, AND (E) RECOVERING A BUNDLE OF ELASTOMERIC FILAMENTS FREE FROM APPRECIABLE INTERFILAMENT ADHESION. 